The present invention relates generally to diesel engines with exhaust systems comprising diesel particulate filters (DPF) and, more particularly, to methods and arrangements for triggering and stopping active regeneration in DPFs.
In diesel engines, it is now typical to use a DPF downstream of the engine to filter particulate from the engine exhaust. If too much soot collects in the DPF, the soot can burn in an uncontrolled manner and may crack or melt the DPF. This phenomenon is sometimes referred to as a “runaway” or uncontrolled regeneration. Other problems can result from excessive soot accumulation in the DPF as well, such as an increase in engine backpressure, which can have an adverse effect on engine operation and affect fuel consumption.
To avoid aforementioned problems such as runaway regenerations, it is common to periodically clean the DPF by burning off the soot, through a so-called active regeneration by O2 oxidation, in a controlled manner that does not damage the DPF. Ordinarily, exhaust systems are configured to perform an active regeneration when soot loading in the DPF filter reaches a level of about 5 g/l (grams per liter). This active regeneration cycle could be triggered by a sensor that measures a particular pressure drop across the DPF that, given a particular soot model for the filter, corresponds to a particular soot loading level. Other events may trigger active regenerations, as well, such as operation for a predetermined length of time.
In the present application, references to “models” of aspects of engine operation are understood to generally refer to simulation software that calculates those operation aspects in real-time or offline based on known engine parameters and/or sensor measurements. The development of such models is well-known in the field of diesel engines; many models relate only to the particular engine for which they were developed, and the development of such models is not intended to form part of the present invention, except as otherwise described herein. Variables or parameters associated with such engine operation models are ordinarily determined through extensive testing of engine operation and the process by which they are determined is also known in the field of diesel engines.
While, in the ideal case, soot should collect uniformly in the DPF, in practice, it does not always do so. Two main causes for non-uniform soot distribution are high flow velocity through the DPF, such as often occurs during highway driving, and so-called passive regeneration, which occurs when NO2 in the exhaust gas oxidizes the soot. Passive regeneration typically occurs at temperatures of about 250° C. to 450° C., which falls at least partially within normal operating temperatures of the DPF. Active regeneration typically occurs at temperatures greater than 550° C.
Triggering of the active regeneration cycle as a function of pressure drop across the DPF assumes a uniform soot distribution. When soot is not uniformly distributed then it is possible that, although the pressure drop across the DPF has not reached a trigger point, some portions of the DPF may have soot loading at or above the level where runaway regeneration can occur, and other portions of the DPF may have soot loading below that level. In other words, in certain conditions, the pressure drop measurements may tend to underestimate actual soot loading on parts of the DPF, which can lead to damage to the DPF.
Once an active regeneration begins, regeneration proceeds according to a regeneration schedule for the filter for a predetermined length of time such that it will be completely or substantially burnt off.
It is desirable to provide a system and method for triggering active regenerations in a DPF where soot loading may be non-uniform. It is also desirable to provide a system and method for triggering the end of active regeneration in a DPF where soot loading may be non-uniform.
In accordance with an aspect of the present invention, a method for maintaining a DPF is provided. According to the method, a pressure drop across the DPF is measured. An initial estimate of soot loading in the DPF is provided to a recursive filter in the preferred embodiment. In another embodiment of the invention, a cost function or a weight function could be used instead. Using the recursive filter, the initial estimate of soot loading is updated in view of the measured pressure drop to provide an updated estimate of soot loading in the DPF. Active regeneration of the DPF is triggered when the earliest one of at least one triggering condition occurs, the updated estimate of soot loading reaching a predetermined value being one of the at least one triggering condition.
In accordance with another aspect of the present invention, a method for estimating soot loading in a DPF is provided. According to the method, a pressure drop across the DPF is measured. An initial estimate of soot loading in the DPF is provided to a recursive filter. Using the recursive filter, the initial estimate of soot loading is updated in view of the measured pressure drop to provide an updated estimate of soot loading in the DPF.
In accordance with another aspect of the present invention, a diesel engine system comprises a diesel engine, a DPF downstream of the engine, a pressure sensor arrangement for measuring pressure drop across the DPF, and a control system. The control system comprises a recursive filter arranged so that, upon provision of a soot loading estimate in the DPF and a measurement by the pressure sensor arrangement of pressure drop across the DPF, an updated soot loading estimate in the DPF is provided, and so that active regeneration of the DPF is triggered in response to at least one triggering condition, the at least one triggering condition including the updated estimate of soot loading.